[CVE-2026-98342][MODERATE 7.0] dmaengine: wait for RCU readers before releasing dma_device [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98342
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: dmaengine: wait for RCU readers before releasing dma_device [ Upstream
Commit: ac8ce9f89638d6d79875cca7d8ae42566a9bde15
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ac8ce9f89638d6d79875cca7d8ae42566a9bde15
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98342
Analysis date: Sat, 10 Oct 2026 08:21:43 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98342 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98342

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98342	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98342 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race between dma_issue_pending_all() and dma_device_release() can cause a reader to access a dma_device after the provider object has been removed from the global list and freed. The confirmed primitive is a use after free because list_del_rcu() was not followed by an RCU grace period before device_release() could call kfree(). A concurrent reader may dereference stale device fields or traverse stale channel data, causing a kernel crash and potentially creating memory corruption if the freed allocation is reused. For the CVSS the PR:L value represents the paranoid case where a restricted local service account, container root, or other delegated user can influence DMA provider teardown or device lifecycle operations. Typical systems require administrative privileges for driver unload or device removal, which is reflected by PR:H in the base score. The race requires a timing window between provider release and the RCU protected traversal, so AC:H is appropriate. The issue is not directly network reachable. Impact is at least a local denial of service via kernel crash and in the worst case may include confidentiality, integrity, and privilege escalation impact through reuse of the freed kernel object.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	HARDWARE KPANIC MEMORY 	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 4
* Applied conservative FLOOR 4: 3 -> 4 because a real RCU UAF reaches an active structured object and host-admin-equivalent privilege is not positively established.
* Applied paranoid FLOOR 4: 3 -> 4. No additional technically grounded paranoid signal is established.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF and lifetime violation. `dma_device_release()` can free a `dma_device` immediately after `list_del_rcu()`, while a pre-existing `dma_issue_pending_all()` RCU reader can still access that object.
* +1 Realistic kernel crash or strong DoS. Dereferencing a freed DMA provider or traversing stale channel state can produce an Oops or kernel crash.
* +0 Concrete RCU referenced-object lifetime mismatch. The direct RCU-listed object itself is freed too early. The separate cross-object A-to-B invariant required for the additional +1 rule is not established.
* +0 Structured stale-object leverage. `dma_device` is active and structured, but attacker-controlled reclaim, replacement contents, callback influence, or another useful post-free mechanism is not demonstrated.
* +0 Repeated release or refcount mutation. No second `put`, `kref_put`, `free`, or equivalent lifetime mutation through the stale reader is shown.
* +0 Local unprivileged trigger. Below-host-admin reachability is not established.
* +0 Remote reachability. No network-controlled path reaches the provider release and concurrent reader sequence.
* +0 Confidentiality or integrity. No disclosure, directed write, controlled reclaim, or protected-state modification is demonstrated.
* +0 Extra availability. The possible crash is already counted and no distinct persistent availability consequence is established.
* No race penalty was applied. The race exists, but the supplied evidence does not establish that it is narrow, one-shot, or materially difficult to repeat.
* No privilege penalty was applied. DMA provider teardown may involve administrative device management, but the complete privilege requirement is unresolved rather than positively proven host-admin-only.
* B5-R is not applicable because no retry-accumulated OOB write exists.
* B3-PENDING is not applicable because no shared-backing write exists.
* B4-PENDING is not applicable because no authorization decision or DENY-to-ALLOW transition exists.

3. Reachability analysis

The vulnerable reader is `dma_issue_pending_all()`, which performs a normal RCU traversal of the global DMA provider list. The conflicting lifetime transition occurs when the final `dma_device` reference reaches `dma_device_release()`, usually as part of provider unregister or driver teardown.

The supplied context does not establish which user-controlled interface, if any, can force both the final release and concurrent reader. It also does not prove that host root or a host-admin-equivalent capability is mandatory for every complete trigger. Therefore `HostAdminRequired=UNKNOWN`, with no privilege penalty.

DMA provider registration and teardown are global kernel and device-management operations rather than user-namespace-scoped operations. No attacker-created namespace can perform the complete sequence based on the supplied evidence, so `NamespaceScopedPrivilege=NO`.

No direct remote path is present. Hardware or a DMA-capable driver is required, but the evidence does not show that the hardware is rare or physical-attacker-only, so no hardware or niche-subsystem penalty is justified. Race repeatability remains unresolved.

4. Primitive and severity interpretation

The exact primitive is a real RCU use-after-free. `list_del_rcu()` removes the provider from future traversals but does not wait for readers that already obtained or reached the object. `device_release()` may then call `kfree()` before those readers finish.

The stale storage is an active structured `dma_device`, not a fixed transfer buffer. The stale use occurs in a normal reader rather than solely inside a destructor. However, the supplied patch does not expose the exact stale fields consumed, demonstrate controlled slab reuse, establish attacker-shaped replacement data, or show callback dispatch from reclaimed contents.

There is no concrete repeated release or refcount operation. The reader accesses the stale object, but it is not shown performing a second lifetime mutation on the same reference. The repeated-release exception and FLOOR 5 therefore do not apply.

This is CLASS_B because an actual kernel object lifetime violation exists. The demonstrated practical consequence is potential kernel crash or DoS. Privilege escalation, disclosure, directed corruption, and controlled execution are speculative and unsupported.

`ImportantCandidate=NO` because the evidence currently supports an uncontrolled RCU UAF without meaningful attacker-controlled reuse or another independent exploitation primitive. `AutoDowngradeAllowed=YES` because no concrete repeated lifetime mutation, controlled reclaim, authorization bypass, or security-boundary violation remains unresolved. Manual review is still recommended because the stale object participates in active DMA subsystem processing and the exact reader operations are not included.

5. One-sentence report phrase

A missing RCU grace period allowed dma_issue_pending_all() to access a freed dma_device during concurrent provider teardown, creating a real kernel use-after-free with a plausible crash consequence but no demonstrated controlled reclaim or privilege-escalation primitive.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review the complete `dma_issue_pending_all()` stale-use path, relevant provider implementations, user-accessible unregister or reset paths, and whether reclaimed `dma_device` or channel fields can influence callbacks, pointers, or DMA operations.

7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: dmaengine: wait for RCU readers before releasing dma_device [ Upstream
Commit: ac8ce9f89638d6d79875cca7d8ae42566a9bde15
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ac8ce9f89638d6d79875cca7d8ae42566a9bde15

Changed files:
  drivers/dma/dmaengine.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ac8ce9f89638d6d79875cca7d8ae42566a9bde15

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98342 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98342

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: unknown
  Paranoid ActionableScore: 4

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).